JavaScript Basic

Programming Basic


Programmers use variables to store values. A variable can hold several types of data. In JavaScript you don'y have to declare a variable's data type before using it. Any variable can hold any JavaScript data type, including :

• String data
• Numbers
• Boolean values (T/F)

Variable Names

There are rules and conventions is naming variables in any programming language. It's good practice to use descriptive names for variables. The following are the JavaScript rules :

• The variable name must start with a letter or an underscore. firstName or _myName
• You can use numbers in a variable name, but not as the first character. name01 or tuition$
• You can't use space to separate characters. userName not user Name
• Capitalize the first letter of every word except the first. salesTax or userFirstName

Variables

• To declare variables, use the keyword var and variable name : 

var userName

• To assign values to variables, add an equal sign and the value : 

var userName="Smith"

var  price=100

Functions


With functions, you can give a name to a whole block of code, allowing you to reference it from anywhere in your program. JavaScript has built-in functions for several predefined operations. Here are three some functions.

• alert("message")
• confirm("message")
• prompt("message")

Functions Example

• Open "functions.html" and View the Source
• Put the cursor after "// add code here" and enter :

var userName
var willDoSurvey
userName=prompt("Enter you name","")
alert("Thank you," + userName)

• Save the changes and Refresh the page

User-Defined functions

With user-defined functions, you can name a block of code and call it when you need it. You define a function  in the HEAD selection of a web page. It's defined with the function keyword, followed by the function name and any arguments.

function functionName(argument)

{ statements }

User-Defined Example

• Open "userdefined.html" and View yhe Source
• Put the cursor after "<!- enter function -->" and enter :

<SCRIPT language="JavaScript">
function showAlert() {
alert("this is a user-defined function.")
}
</SCRIPT>

• In the BODY, put the cursor after "<! enter the button def here ->" and enter :

<INPUT type-"button" value="Run the Function" onClick="showAlert()">

• Save the changes and Refresh the browser.

RUN THE FUNCTION

SEE VIDEO

source video : www.youtube.com

Posted in: JavaScript Tutorial